Aluminum-lithium-xanti-fouling coatings

ABSTRACT

An aluminum/lithium/x formulation for steel, plastic, wood, aluminum and the like utilizing, as a pigment, particles of aluminum/lithium/x dust from 1 micron to 100 microns (0.04 mils to 4.0 mils) having a ratio of 0.1 to 6.0 percent of lithium to 99.9 to 94.0% aluminum. Other (x) alloying materials may be magnesium, copper and the like. Said pigment is resistant to fouling by barnacles and the like. Heat treating the aluminum-lithium alloy surface produces lithium at 10 percent or above thus making the surface toxic or repellent to many bacteria and higher trophic organisms. The aluminum-lithium alloy contains no toxic heavy metals and is generally environmentally benign and leach resistant.

CROSS REFERENCED TO RELATED APPLICATIONS

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FEDERAL FUNDING

N/A BACKGROUND OF Invention

For years it was necessary to take ships out of the water to scrape the bottoms to remove barnacles and other growth because it affected the ship's performance. Copper, lead, and zinc have been used to prevent the growth successfully but have been proved to be environmentally unacceptable. In this invention we substitute lithium for all of these heavy metals producing a growth inhibitor that is environmentally safe. Pure lithium metal is highly reactive, however as a component of an alloy it functions well, does not leach, and is stable in the alloy.

Aluminum/Lithium/X Anti-Fouling Coating

SUMMARY OF DISCLOSURE

This invention relates to improvements in coating compositions utilized to form protective coatings on surfaces which reduce bio-film attachment to structures exposed to water. Bio-fouling degrades marine structures in both saltwater and fresh water environments. The pigment is effective against zebra mussels in fresh water and barnacles in saltwater.

In another application the micro-fine flakes may be used to protect objects exposed to soil and other damp environments such as telephone poles, sign posts and railroad ties, by coating or impregnating them.

The micro-fine flakes may also be applied in a suitable coating vehicle such as epoxy paints in ducts and conduits for cooling or irrigating waters.

A particular advantage of the pigment is that the system of aluminum and lithium is free of heavy metals which have serious consequences in the environment. Elements such as lead, chromium, and cadmium have serious impacts on health. Lighter elements are generally less offensive to the environment.

Another advantage of the aluminum-lithium pigments is that they provide corrosion resistance for steel and aluminum substrates. These advantages are covered in U.S. Pat. No. 6,069,197 by the same author of this invention. While it is usually required that metal filled paints be stirred during application to prevent settling, aluminum-lithium is light due to the low molecular weight, so that stirring is generally not required during application.

While copper and certain copper compounds are effective as well, they are heavy metals and prohibited frequently as pollutants in the waters of many harbors. While aluminum and lithium are effective against bacteria and hence prevent the onset of the fouling sequence (which begins with bacteria and culminates in barnacles and zebra mussels and the like) they are also very light metals and therefore do not cause the pollution problems of copper.

Not only is aluminum-lithium more ecologically acceptable, tests showed effective biocidal action indicating it's use to prevent bio-fouling in open waters as well as closed environments.

The metallic pigment may be applied in sheets, flakes, or powder form. The flake and powder held in a suitable system such as epoxy resin and the like at a ratio and in a fashion as to make the metal particles available to the contaminant bacteria. Two such methods are in inorganic silicate vehicles and in porous organic configurations. Another technique is to simply use a high pigment loading.

The composition of the instant invention may also contain compatible filler to influence properties such as color, adhesion, wetting, ease of manufacture, can stability, and ease of application, so long as these additives do not adversely affect the desired characteristics.

The aluminum-lithium also exhibits enhanced performance by the heat treatment described in U.S. Pat. No. 6,069,197 by the same author of this invention. Heating the aluminum-lithium to 350° C. for fifteen minutes produces a migration of the lithium to the surface of the alloy thereby improving the available lithium in the alloy at or near to the surface.

Having described the general details of the invention, the following formulations are presented as typical coatings for the anti-fouling, antibacterial, bio-film producing coatings therein.

The aluminum-lithium pigment used was: 260 mesh powder with 1% lithium, 6.8% magnesium and 92.2% aluminum.

It was heat treated under an argon blanket for 15 minutes at 350° C. as per U.S. Pat. No. 6,069,197. Although the pigment is effective without the heat treatment, the performance is enhanced by heating. Heating for longer than 15 minutes or at higher temperatures than 350° C. begins to make the treatment less effective and at the extremes of 400° C. to 500° C. the lithium is nearly depleted from the alloy. Other alloying metals with the aluminum which have been incorporated at 7% or less such as magnesium, copper, zinc and the like do not greatly change the lithium function. Increasing the concentration of lithium at the surface of the alloy makes the surface more alkaline. At pH's above 10 or so these surfaces are toxic to bacteria. The deposition of bacteria can be the first step in a sequence of nutrients for progressively larger flora and fauna food chains. Work done at Louisiana State University by Dr. Ralph Portier, et. al. in the “Materials Performance” publication dated October 2004 provides more details on this phenomenon. Thus copper flakes and aluminum-lithium flakes make superior anti-fouling materials and resist the deposition of barnacles, zebra mussels and algae. However the copper is considered an environmental problem as a heavy metal.

The following are specific formulations made in accordance with the instant invention.

EXAMPLE I FOR STEEL SUBSTRATE

Component Parts by Weight Lithium Silicate 100 Aluminum-Lithium Powder 240 mesh (92.2% alumi- 59.4 num, 6.8% magnesium, 1.0% Lithium) Mica (325 mesh) 7.5 Lithium Molybdate 0.5 Sodium Borate Decahydrate 0.4 Total 167.8

EXAMPLE II FOR ALUMINUM SUBSTRATE

Component Parts by Weight Aluminum-Lithium Powder 240 mesh 64.5 Potassium Silicate Solution 60 Total 124.5

EXAMPLE III FOR GENERAL USE

Component I-RESIN Parts by Weight Resin BisPhenol Epoxy 42.7 Aluminum-Lithium 260 Mesh 123.1 Epoxy Diluent 34.5 Benzyl Alcohol 8.6 Total 208.9 (the formula in example III is a solvent-less 2-component epoxy)

Component II -CATALYST Parts by Weight Polyamide Curing Agent 22.6 Mica (320 Mesh) 22.7 AEP Tertiary Amine 11.4 Total 56.7

Although the composition of this invention is described with reference to preferred embodiments thereof, it will be apparent from the foregoing description that numerous variations and modifications can be made in the composition without departure from the information, and it should be understood that the scope of the invention is limited only by the following claims. 

1. An aluminum-lithium alloy dust formulation for protecting steel, aluminum, wood and the like from the bio-fouling damage.
 2. An aluminum-lithium alloy dust formulation which in both fresh and salt water discourages the set down of mussels and barnacles and the like on surfaces in immersion.
 3. An aluminum-lithium alloy dust with the pH at the surface of the alloy at pH 10 or above and consequently repulsive to bacteria and some higher trophic organisms.
 4. The material in claim 1 where the lithium is 0.1 to 6.0 percent by weight of the aluminum-lithium alloy.
 5. The material in claim 1 where the alloy of aluminum-lithium has been heated to 300° C. to 350° C. under an inert gas atmosphere for 10 to 15 minutes thereby concentrating the lithium on the surface of the alloy.
 6. The material in claim 3 where the hygienic protection facilitates sanitary decontamination of surfaces.
 7. The material in claim 3 where the lithium in the aluminum-lithium alloy is 0.1 to 6.0 percent by weight.
 8. The material in claim 3 where the alloy of aluminum-lithium has been heated to 300° C. to 350° C. for 10 to 15 minutes in an inert atmosphere thereby concentrating the lithium at the surface of the alloy. 